Magnetic properties of the youngest sapropel S1 in the Ionian and Adriatic Sea: inference for the timing and mechanism of sapropel formation

Luigi Vigliotti(*), Alessandra Asioli(**), Caterina Bergami(*), Lucilla Capotondi(*) & Andrea Piva(***)
(*) ISMAR-CNR, Via P. Gobetti, 101 - 40129 Bologna, Italy. Corresponding author: Luigi Vigliotti (luigi.vigliotti@bo.ismar.cnr.it tel.: 051-6398877, fax: 051-6398940). (**) IGG-CNR, Padova, Italy. (***) Eni S.p.A. - E&P Division, 20097 San Donato Milanese (MI) Italy.

The youngest sapropel S1 has been investigated by a multiproxy study on a core (ET99-M11) collected in the western Ionian Sea at a water depth of 2800 m, which is considered to represent anoxic conditions in the eastern Mediterranean at the time of sapropel formation. Selected geochemical parameters (TOC, Ba/Al, MnO) as well as micropaleontological analysis (planktic foraminifera), rock magnetic data, and 14C dating indicate that anoxic conditions prevailed between 10.4 and 5.7 ka BP. The comparison among the different proxies indicates that rock magnetic parameters can be unambiguously used to precisely identify sapropel layers, even if no iron sulphide phases have been precipitated as a bi-product of diagenetic breakdown of organic matter. By using the magnetic parameters as indicators of paleoredox conditions we compare the results with cores collected in the central and southern Adriatic Sea at different water depths. A shorter duration (9.6/9-7/6.8 ka BP) of the sapropel S1 was observed in the deepest southern part of the basin and in the Meso Adriatic Depression whereas suboxic conditions continued in cores collected at very shallow water depth of 56 m along the western margin of the basin. The formation of the Adriatic Deep Water driven by decreasing solar radiation output is considered responsible for the interruption and end of sapropel formation.

Sapropel, Sediment, Magnetic Properties, Foraminifera, Central Mediterranean, Holocene.